The use of certain organofluorine derivatives as additives for lubricating compositions is known; for example the use of salts of aliphatic amines and of perhalogenated monocarboxylic acids such as the acid Cl(CF.sub.2 CFCl).sub.3 CF.sub.2 COOH and the acid C.sub.7 F.sub.15 COOH has been described in U.S. Pat. No. 3,565,926, just as the use of the derivatives obtained by reacting an aromatic amine and a perfluorinated monocarboxylic acid (for example C.sub.7 F.sub.15 COOH) has been disclosed in Patent FR 2,026,493. However, these carboxylic derivatives have the disadvantage of losing their antiwear effectiveness in the presence of conventional additives such as dispersant-detergent additives, either as a result of physicochemical interactions which prevent their absorption at the surfaces to be lubricated, or because of chemical interactions, in particular when the dispersant-detergent additives are neutral or overbased salts of alkaline-earth metals.
The use of amines or of aminoalcohols containing a polyfluorinated chain (Patent FR 2,520,377) and that of derivatives of these aminoalcohols (Patents FR 2,599,378, 2,616,781 and 2,616,783) as antiwear additives for lubricants has also been proposed.
There are also known certain polyfluorocarboxylic acids of formulae: EQU R.sub.F (CH.sub.2).sub.10 COOH (I) ##STR2## in which R.sub.F denotes a perfluoroalkyl radical.
The use of these acids or of their derivatives as additives for lubricants does not appear to have yet been envisaged. According to U.S. Pat. No. 2,951,051, which describes 11-(perfluorooctyl)undecanoic acid, its sodium and potassium salts and its chromium complex (Examples II and V), the monocarboxylic acids (I) are prepared from 10-undecenoic acid and a perfluoroalkyl sulphochloride or iodide. U.S. Pat. No. 4,107,055, relating to the use of diacids and of their alkali metal salts as fluorinated surface-active agents in antisoiling compositions based on unhalogenated polymer latexes for textiles, indicates that the diacids (II) can be prepared by the action of zinc on the iodoacids R.sub.F CH.sub.2 CHI(CH.sub.2).sub.m COOH in ethanol.